Tayyib Muhammad, Svilainis Linas
Department of Electronics Engineering, Kaunas University of Technology, 51368 Kaunas, Lithuania.
Sensors (Basel). 2025 Jan 5;25(1):265. doi: 10.3390/s25010265.
The application of spread-spectrum signals (arbitrary pulse width and position (APWP) sequences) in air-coupled resonant ultrasound spectroscopy is studied. It was hypothesized that spread-spectrum signal optimization should be based on te signal to noise ratio (SNR). Six APWP signal optimization criteria were proposed for this purpose. Experimental measurements were conducted using a thin polycarbonate sample using two standard spread-spectrum signals, linear and nonlinear frequency modulation, together with six optimized APWP signals. It was found that the performance of APWP signals derived from linear frequency modulation was better. The two best performing optimization criteria are SNR improvement on a linear scale with the SNR as an additional weight and energy improvement on a dB scale. The influence of spectral coverage on measurement errors was evaluated. It was found that it is sufficient to cover the sample resonance peak and the valley. The lowest error rates for density, 3%, and for thickness, 3.5%, were achieved when the upper valley was covered. For velocity, the best result, 5%, was achieved when the lower valley was covered. The lowest error rate for attenuation, 3.8%, was achieved in the case when both valleys were covered. Yet no significant performance degradation was noted when a whole -30 dB passband was covered.
研究了扩频信号（任意脉冲宽度和位置（APWP）序列）在空气耦合共振超声光谱中的应用。假设扩频信号优化应基于信噪比（SNR）。为此提出了六个APWP信号优化标准。使用薄聚碳酸酯样品，采用两种标准扩频信号（线性和非线性频率调制）以及六个优化的APWP信号进行了实验测量。发现由线性频率调制得到的APWP信号性能更好。表现最佳的两个优化标准是在以SNR为附加权重的线性尺度上提高SNR以及在dB尺度上提高能量。评估了光谱覆盖范围对测量误差的影响。发现覆盖样品共振峰和谷就足够了。当覆盖上谷时，密度的最低误差率为3%，厚度的最低误差率为3.5%。对于速度，当覆盖下谷时获得了最佳结果5%。当两个谷都被覆盖时，衰减的最低误差率为3.8%。然而，当覆盖整个-30 dB通带时，未观察到明显的性能下降。
